Magnetron output coupling circuit



July 26, 1960 P. W. CRAPUCHETTES MAGNETRON OUTPUT COUPLING CIRCUIT Filed Dec. 18,1950

x x fi M .hlll' A\ M INVENTOR CRAPUC HE TTE5 ATTORNEY United States Patent MAGNETRON OUTPUT COUPLING CIRCUIT Paul W. Crapuchettes, Palo Alto, Calif., assignor to Litton Industries, Inc.

Filed nears, 1950, Ser. No. 201,412

'3 Claims. on. 3-15-39 more particularly to such output coupling circuits used for multi-oavity magnetrons.

In certain types of electron discharge devices wherein cavity resonators are excited by the passage of electrons past openings in the resonators, coupling circuits have been provided by an opening from one or more of the resonators into the wave guide, one end of which is terminated in a window of dielectric material such as glass for example. This technique has been used in high frequency magnetrons where wave guide output was desired. In such types of magnetrons considerable difliculty has been encountered in that the free electrons sometimes stray into the resonators and may be projected at relatively high velocity through the opening into the wave guide so as to impinge upon the insulating window. This causes rupture of the window permitting leakage of gas into the tube and destroying the tube.

One solution for this problem is described in previous U.S. patent to Mr. C. V. Litton No. 2,477,633 granted August 2, 1949, entitled, Blocking Means for Electron Discharge Devices. According to this patent the difficulty is minimized by providing magnetic means to divert stray electrons which have entered into the wave coupler for a cavity resonator into a wave guide havingv a dielectric output window wherein the structure of the output opening is such that free electrons will be inherently directed toward the wall of the wave guide so as to avoid impingement upon the output window.

According to a feature of my invention I provide a coupler circuit for a cavity resonator, arranged for excitation by free electrons, coupled to a wave output circuit wherein a communicating slot between the resonator and the wave guide is made in the outer wall of the resonator aligned to. direct free electrons passing through the slit toward the wave guide wall.

According to a further feature of my invention I provide an output coupling circuit for a multi cavity resonator magnetron in which the magnetron resonators consist of relatively thin radially disposed vanes connected to a relatively thick cylindrical wall, the coupling comprising a wave guide having its longitudinal outer conductive wall sealed at one end to the outer wall of the resonators. An insulating window is sealed at the other end of the wave guide and a communicating slit is made between the resonator and the outer wave guide. This slit is non-radial with the cylindrical wall and at an angle to the wave guide wall to direct the electrons which may pass through the slit toward the wave guide wall.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be Patented July 26, 1960 best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, in which:

The single figure illustrates a cross-sectional view of a portion of the magnetron showing the coupling arrangement between the resonators thereof and the output wave guide.

Turning to the drawing there is illustrated a magnetron having an exciting cathode 1 disposed centrally of a cylindrical outer wall 2. A plurality of radially disposed vanes 3 are -fastened at one end to wall 2 to provide successive adjacent cavity resonators. Strapping rings 4 and 5 may be provided to minimize mode-jumping as is usual practice in this type of magnetron. The resonator wall portion 2 may be further surrounded by the outer magnetron body cylinder 6. Coupled to the magnetron is an output wave guide 7 comprising a conductive outer wall member 8 which may be cylindrical or rectangular in shape sealed at one end 9 to the body portion 6. At the other end of wave guide 7 there is provided a window 10 of dielectric material which may be glass, for example, so that the electro-magnetic waves in the wave guide may be applied to any desired output circuit. As illustrated, window 10 is mounted in a supporting ring 11 .which may be soldered or brazed to a second ring 12 sealed to the outer wall 8 of wave guide 7. A coupling threaded ring 13 may be supplied for fastening an output wave guide line if desired. Impedance transformer ramps 14 may be also supplied to match the impedance of the wave guide with the impedance of the magnetron resonator. The magnetron resonator and the output wave guide are coupled by means of an opening such as slit .15 made in the outer resonator wall 2. This slit 15 is longitudinally disposed in the cylindrical wall 2 at a non-radial angle. The walls of the slit being so directed that the output angle subtended therefrom will terminate in Walls 8. It will, therefore, be clear that any electrons leaving the resonator and entering the wave guide will be directed so as to be intercepted by the wave guide wall 8. Since this wave guide wall and the resonator structure operates as an anode and is positive with respect to the cathode, any electrons impinging thereon will be captured and will, therefore, not be able to reach window 10.

It will be noted that electrons leaving the resonator will ordinarily fall within the angle defined by dotted line 16, 17. This is true since the higher velocity of electrons tend to travel in a straight line. Any lower velocity electrons will be attracted by the positive potential to the walls in any case. Furthermore, low velocity electrons would not cause damage even if they impinged upon window 10. The most probable path any free electrons leaving the resonator structure would be along line 18 which represents the angle of" slit 15 which respect to wall 8.

While I have illustrated slit 15 as being rectilinear, this being the most practical form, it is clear that the principles of my invention do not depend-upon rectilinearity of such slit. It will readily be understood that the principles of my invention apply equally well to openings of other forms so long as they are arranged to direct free electrons toward the walls 8 of wave guide 7 and away from window 10.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

1. An output coupling circuit for a cavity resonator arranged for excitation by free electrons, said resonator having a substantially cylindrical outer wall, said coupling circuit comprising a wave guide having a conductive wall sealed at one end to said outer Wall, the aXiS of said wave guide being substantially radial with respect to said outer 'Wall, said resonator outer Wall being provided with a communicating opening betweensaid resonator and said Wave guide aligned to direct free electrons passing/through said opening at an angle to said axis and toward said wave guide wall.

2. A coupling according to claim 1, wherein the other end of said wave guide is terminated by an insulating window whereby electro-magnetic waves in said wave guide may be applied to external circuits.

3. An output coupling circuit for a multi-cavity resonator magnetron, wherein the magnetron resonators are composed of relatively thin radially disposed vanes connected to a relatively thick outer cylindrical wall, comprising a'wave guide having longitudinal conductive walls sealed at one end to said outer-wall, an insulating window sealed to the other end to said conductive walls, said outer cylindrical wall having a communicating open slit :between one of said resonators and the interior of said wave guide positioned at an angle to a radius of said cylinder and to said conductive wall, whereby free electrons passing through said slit will be directed toward one of said conductive walls.

References Cited in the file of this pat ent UNITED STATES PATENTS 2,412,772 Hansell l Dec. 17, 1946 2,429,291 O kressco Oct. 21, 1947 2,466,765 Hartman Apr. 12, 1949 2,555,349 Litton June 5, 1951 2,559,582 Bailey July 10, 1951 2,564,716 Okress Aug. 21, 1951 

